Assessing the range of blasting-induced cracks in the surrounding rock of deeply buried tunnels based on the unified strength theory

Blasting-induced cracks in the rock surrounding deeply buried tunnels can result in water gushing and rock mass collapse,posing significant safety risks.However,previous theoretical studies on the range of blasting-induced cracks often ignore the impact of the in-situ stress,especially that of the intermediate principal stress.The particle displacement−crack radius relationship was established in this paper by utilizing the blasthole cavity expansion equation,and theoretical analytical formulas of the stress−displacement relationship and the crack radius were derived with unified strength theory to accurately assess the range of cracks in deep surrounding rock under a blasting load.Parameter analysis showed that the crushing zone size was positively correlated with in-situ stress,intermediate principal stress,and detonation pressure,whereas negatively correlated with Poisson ratio and decoupling coefficient.The dilatancy angle-crushing zone size relationship exhibited nonmonotonic behavior.The relationships in the crushing zone and the fracture zone exhibited opposite trends under the influence of only in-situ stress or intermediate principal stress.As the in-situ stress increased from 0 to 70 MPa,the rate of change in the crack range and the attenuation rate of the peak vibration velocity gradually slowed.

Mechanical and damage evolution properties of sandstone under triaxial compression

To study the mechanical and damage evolution properties of sandstone under triaxial compression, we analyzed the stress strain curve characteristics, deformation and strength properties, and failure process and characteristics of sandstone samples under different stress states. The experimental results reveal that peak strength, residual strength, elasticity modulus and deformation modulus increase linearly with confining pressure, and failure models transform from fragile failure under low confining pressure to ductility failure under high confining pressure. Macroscopic failure forms of samples under uniaxial compression were split failure parallel to the axis of samples, while macroscopic failure forms under uniaxial compression were shear failure, the shear failure angle of which decreased linearly with confin- ing pressure. There were significant volume dilatation properties in the loading process of sandstone under different confining pressures, and we analyzed the damage evolution properties of samples based on acoustic emission damage and volumetric dilatation damage, and established damage constitutive model, realizing the real-time Quantitative evaluation of samnles damage state in loading process.

Effects of joint persistence and testing conditions on cyclic shear behavior of en-echelon joints under CNS conditions

Cyclic shear tests on rock joints serve as a practical strategy for understanding the shear behavior of jointed rock masses under seismic conditions.We explored the cyclic shear behavior of en-echelon and how joint persistence and test conditions(initial normal stress,normal stiffness,shear velocity,and cyclic distance)influence it through cyclic shear tests under CNS conditions.The results revealed a through-going shear zone induced by cyclic loads,characterized by abrasive rupture surfaces and brecciated material.Key findings included that increased joint persistence enlarged and smoothened the shear zone,while increased initial normal stress and cyclic distance,and decreased normal stiffness and shear velocity,diminished and roughened the brecciated material.Shear strength decreased across shear cycles,with the most significant reduction in the initial shear cycle.After ten cycles,the shear strength damage factor D varied from 0.785 to 0.909.Shear strength degradation was particularly sensitive to normal stiffness and cyclic distance.Low joint persistence,high initial normal stress,high normal stiffness,slow shear velocity,and large cyclic distance were the most destabilizing combinations.Cyclic loads significantly compressed en-echelon joints,with compressibility highly dependent on normal stress and stiffness.The frictional coefficient initially declined and then increased under a rising cycle number.This work provides crucial insights for understanding and predicting the mechanical response of en-echelon joints under seismic conditions.